Pivoted tensioner levers have been widely used for maintaining tension in transmission chains used as timing chains in internal combustion engines. These levers have shoes that are in sliding contact with a portion of the transmission chain, and are typically pivoted on shoulder bolts secured to the engine block.
As shown in FIG. 6, for example, a typical conventional tensioner lever 500 comprises a shoe 510, in sliding contact with a chain C traveling along the longitudinal direction of the lever. The back side of the shoe is engaged with, and supported by, an elongated lever body 520, having a boss 530 adjacent its proximal end, i.e., the end that is first contacted by the traveling chain as the chain approaches the lever. As shown in FIGS. 7 and 8, the lever is mounted on an inner wall of an engine E by means of a shoulder bolt SB, having a cylindrical part Sr that extends through a cylindrical hole in the boss 530. For further details of the typical conventional tensioner lever, reference may be made to British patent application 2 351 136, published Dec. 20, 2000.
When the lever is mounted on the shoulder bolt, a part of the outer circumferential surface of the cylindrical part Sr of the shoulder bolt is exposed. The tensioner lever can be mounted so that it extends upward from the location of the shoulder bolt on which it is pivoted. Therefore, engine oil 0 (FIG. 6) adhering to the lever body 510 can flow into the narrow region between the outer circumferential surface of the cylindrical part Sr of the bolt, and the inner surface of the cylindrical hole in the boss 530. However, when the boss 530 of the conventional tensioner lever is in contact with an inner wall of an engine E as shown in FIG. 7, or in contact with the flange Sf of a shoulder bolt SB, as shown in FIG. 8, oil can flow into the space between the bolt and the inner surface of the boss from only one end of the boss, and there is insufficient room for oil to flow into this space from the opposite end of the boss. As a result, galling, seizing, and asymmetric, i.e., one-sided, wear of the mounting bolt and the interior of the boss, can occur due to insufficient lubrication, and early failure of the tensioner lever can occur. Furthermore, friction between the boss 530 and the outer circumferential surface of the cylindrical portion Sr of the bolt SB, can prevent the tensioner lever from reliably following and responding to changes in tension in the transmission chain C.